Oak wilt fungus lethal to oaks, spreads through roots

By MINDY POEHL | Central Texas Edition

Renee Burks, with the Texas Forest Service, holds an i.v. that is used to inject oak trees with medicine to protect their roots against the oak wilt fungus. Photo by Mindy Poehl

July 29, 2004 - Oak trees are thick, attractive trees that provide shade and beauty to lawns. They also provide food and homes to animals. Oak trees can also be home to the oak wilt virus, which can destroy the trees.

Oak wilt is a lethal disease caused by the fungus Ceratocystis fagacearum. The fungus invades and disables the water-conducting system in live oaks, Spanish oaks, red oaks and other oaks.

Killing oak trees at epidemic quantities in Central Texas, oak wilt is centrally located in Central Texas, but is also found in Lubbock, Amarillo and San Angelo. Deer hunters recently spread the disease to Houston, said Renee Burks, Texas Forest Service Project Forester with the Texas Forestry Service.

Oak wilt spreads quickly through the roots grafts that connects trees of the same species growing near one another. It can also be carried by insects, like the beetle.

Burks spoke about oak wilt control and prevention at MCC Highlander Ranch on July 21. Burks said the fungus can spread from diseased trees, so use a disinfectant, such as Lysol, on any tools that touch the tree. Man spreads the oak wilt fungus by moving wood from infected red oaks to other locations.

Live oaks grow in large, dense groups with connecting roots. Root transmission is the only proven way of spreading in live oaks. As a result, patches of dead and dying trees, also called infection centers, are formed. Infection centers in live oaks expand at an average of 50 feet per year, Burks said. Oak wilt is easy to identify in live oaks by veinal necrosis in the leaves. The veins on the leaves are discolored and pop out. Oak wilt begins in the canopy and works its way down, and it progresses in a six week to six month period. Some live oaks may survive the fungus.

Red oaks play a key role in the establishment of new infection centers. One in ten red oaks produces oak wilt, Burks said. Oak wilt looks different on red oaks. The leaves have a red, scalded look and they wilt. The disease progresses in seven to 10 days and almost no red oaks can survive the fungus.

Three primary forms of disease management exist. The first approach is to prevent the formation of a new oak wilt virus infection centers by eliminating infected red oaks, handling firewood properly and painting wounds on healthy oak trees. The second approach involves injections of a fungicide into the tree.

"It's like hooking a big i.v. up to the tree," Burks explained.

The third approach involves disrupting the root connections by trenching. Burks forms five foot deep trenches 100 feet around the infected and nearby trees.

Burks advised, "Don't cut down a sick tree because it speeds up the time frame of the disease movement. Oak wilt will hit a healthier tree harder than an unhealthy one."